Methods of applications for a mass spectrometer in combination with a gas chromatograph

ABSTRACT

Methods may include emplacing a wellbore tool in a wellbore, the wellbore tool including a gas chromatograph and a mass spectrometer, wherein the mass spectrometer is configured to operate at a pressure greater than 10 −2  Torr, measuring a sample from the wellbore using the wellbore tool, and determining a molecular weight of one or more components of the sample from the measured response of the wellbore tool. Methods may also include establishing a library of one or more chemical components, emplacing a wellbore tool in a wellbore, the wellbore tool including a gas chromatograph and a mass spectrometer, wherein the mass spectrometer is configured to operate at a pressure greater than 10 −2  Torr, measuring a sample from the wellbore using the wellbore tool, comparing the measured response from the wellbore tool for the sample with results from the library of one or more chemical components, and determining a molecular weight of one or more components of the sample.

BACKGROUND

As a wellbore is being prepared, samples of formation fluids may beobtained from downhole and analyzed onsite or sent to a full-scalelaboratory. Analysis of the formation fluids may be beneficial for avariety of reasons including quantifying the quality and amount of thefluids and gasses entering the wellbore, assessing wellbore conditionsfor equipment installation downhole, and ensuring safe well siteoperation. The use of downhole measurement tools may be employed asoperators seek to eliminate the need to obtain and transport samples ofthe formation fluids to the laboratory for further detailed analysis.

The analysis of wellbore fluids and gasses onsite may provideinformation about the maturity and nature of hydrocarbons in theaccumulated source, compartmentalization of intervals in the reservoirbeing drilled, and oil quality, as well as information regardingproduction zones, lithology changes, history of reservoir accumulation,or seal effectiveness. However, downhole analysis using wellbore toolsmay be complicated by a number of factors. Wellbores may be smalldiameter holes having a diameter of approximately five inches or lesswhen cased, which may constrain the geometry of the wellbore toolcomponents. In addition, operating conditions for wellbore tools may bestringent, requiring designs that endure vibrations, elevatedtemperatures and high pressure environments.

SUMMARY

This summary is provided to introduce a selection of concepts that aredescribed further below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In one aspect, embodiments of the present disclosure are directed tomethods that include positioning a wellbore tool in a wellbore. Thewellbore tool includes a gas chromatograph, a rotary valve configured toinject a fluid sample into the gas chromatograph, and a massspectrometer. The mass spectrometer is configured to operate at apressure greater than 10⁻² Torr and an inlet for the mass spectrometerreceives an output from an outlet of the gas chromatograph. The massspectrometer includes at least one of (a) an ion trap analyzer and (b) aquadrupole mass analyzer. The example methods further include measuringa sample from the wellbore using the wellbore tool, and determining amolecular weight of one or more components of the sample from themeasured response of the wellbore tool. 1.

In another aspect, embodiments of the present disclosure may be directedto methods that include establishing a library of one or more chemicalcomponents and positioning a wellbore tool in a wellbore. The wellboretool includes a gas chromatograph, a rotary valve configured to inject asample into the chromatograph, and a mass spectrometer that isconfigured to operate at a pressure greater than 10-2 Torr and includesat least one of (a) an ion trap analyzer and (b) a quadrupole massanalyzer. The example methods include measuring a sample from thewellbore using the wellbore tool, comparing the measured response fromthe wellbore tool for the sample with results from the library of one ormore chemical components, and determining a molecular weight of one ormore components of the sample.

Other aspects and advantages of the disclosure will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a schematic depicting a wellbore tool in accordance withembodiments of the present disclosure.

FIG. 2 is a schematic depicting a wireline tool in accordance withembodiments of the present disclosure.

FIGS. 3 and 4 are flow diagrams indicating various tool configurationsin accordance with embodiments of the present disclosure.

FIG. 5 is a schematic representations of combined gas chromatograph andmass spectrometers in accordance with embodiments of the presentdisclosure.

FIGS. 6.1 and 6.2 are schematic representations of a quadrupole massanalyzer in accordance with the present disclosure.

FIG. 7 is a schematic representation of a ion trap mass analyzer inaccordance with embodiments of the present disclosure.

FIG. 8 is a schematic representation of a cylindrical ion trap massanalyzer in accordance with embodiments of the present disclosure.

FIG. 9 is a flow diagram indicating a mode of measuring the mass of asample component by adjusting operating pressure in accordance withembodiments of the present disclosure.

FIG. 10 is a flow diagram indicating a mode of measuring the mass of asample component by adjusting radio frequency (RF) in accordance withembodiments of the present disclosure.

FIG. 11 is a mass chromatogram of a non-biodegraded oil sample inaccordance with embodiments of the present disclosure.

FIG. 12 is a mass chromatogram of a biodegraded oil sample in accordancewith embodiments of the present disclosure.

FIG. 13 is a graphical representation of the total ion count for asample in accordance with embodiments of the present disclosure.

FIGS. 14-15 are graphical representations of the specific ionmeasurement at 58 m/z for a sample in accordance with embodiments of thepresent disclosure.

FIG. 16 is a graphical representation of specific ion measurement at 58m/z, 72 m/z, and 86 m/z for a sample in accordance with embodiments ofthe present disclosure.

FIG. 17 is a graphical representation of specific ion measurement at 58m/z, 72 m/z, 86 m/z, and 100 m/z for a sample in accordance withembodiments of the present disclosure.

FIGS. 18-20 are mass spectra of three C7 components eluting at 786, 792,and 797 RF, respectively, for a sample in accordance with embodiments ofthe present disclosure.

DETAILED DESCRIPTION

This disclosure relates generally to methods and tools for analyzingformation fluid and gas compositions. More particularly, this disclosurerelates to the determination of a formation fluid composition using agas chromatograph and a mass spectrometer. Mass spectrometers inaccordance with the present disclosure may be configured to operate atrelatively high pressures, such as above 10⁻³ Torr. In one or moreembodiments, instrument components in accordance with the presentdisclosure may have small overall footprints that allow the componentsto be installed in downhole tools.

Devices in accordance with the present disclosure may be configured forcombined gas chromatography and mass spectroscopy optimized forrelatively high pressure operation. Gas chromatographs usechromatographic columns to separate molecular species within a samplefluid and thereby to extract information about the sample fluid. Achromatographic column has a stationary phase fixed inside the columnand a mobile phase which is a carrier gas, such as, helium that flowsthrough the column. The sample is collected, injected into the columnand then transported by the carrier gas into and through the column. Ifthe sample is in a liquid state, the sample may first be injected into avaporization chamber to be vaporized then transported through thecolumn. As a sample progresses through the column, the individualmolecular components are slowed down based on their affinity to thestationary phase. At the outlet of the column, a detector measures thequantity of each component as it exits the column. The calibratedretention time, i.e., the time a component spends in the column,identifies the component.

In one or more embodiments, devices may include a gas chromatograph maybe used in combination with a detector such as a thermal conductivitydetector (TCD). Standard GC-TCD configurations may have a detectionlimit of about 500 ppm, which may be limited in resolution and lack theability to identify individual components of fluids and gases detecteddownhole. In some embodiments, a mass spectrometer may be used incombination with GC-TCD to identify additional fluid and gas components,and may increase measurement sensitivity and lower detection limits ofthe device. Lower detection limits for hydrogen sulfide, mercaptans,corrosion-inducing agents, and oxidants may increase worksite safety andenable an operator to make informed decisions about selection ofwellbore casing and other tools depending on expected levels ofoxidative materials present within a given wellbore.

Devices in accordance with the present disclosure may be configured aspart of a downhole tool. While standard mass spectrometers may useturbo-molecular pumps to generate molecular flow conditions such asbelow 10⁻⁴ Torr, the pumps used to achieve these pressures arevulnerable to shock and vibration, and malfunctions of rotors and orbearings under high pressure, high temperature conditions, and corrosionin the presence of oxidants and other incompatible chemicals that may bepresent in wellbore fluids. However, devices in accordance with thepresent disclosure may be configured to be more robust against shock andvibration and to withstand higher operating temperatures thanencountered in surface measurements, such as those present in a downholeenvironment. For example, operation at higher pressures above >10⁻³ Torrmay enable mass spectrometers in accordance with the present disclosureto perform using scroll pumps and other components design to operateunder harsh conditions.

In one or more embodiments, wellbore tools in accordance with thepresent disclosure may include a testing-while-drilling. With particularrespect to FIG. 1, a testing-while-drilling device 100 may be providedinto a wellbore, which may include a stabilizer with one or more blades110 configured to engage a wall of the wellbore 110. Thetesting-while-drilling device 100 may be provided with a plurality ofbackup pistons 124 configured to assist in applying a force to pushand/or move the testing-while-drilling device 100 against the wall ofthe wellbore 102. A probe assembly 114 may extend from the stabilizerblade 110 of the testing-while-drilling device 100. The probe assembly114 may be configured to selectively seal off or isolate selectedportions of the wall of the wellbore 102 to fluidly couple to anadjacent formation 117. Thus, the probe assembly 114 may be configuredto fluidly couple components of the testing-while-drilling device 100,such as pumps 126 and/or 118, to the adjacent formation 117. Once theprobe assembly 114 fluidly couples to the adjacent formation 117,various measurements may be conducted. For example, a pressure parametermay be measured by performing a pretest. Alternatively, or additionally,a sample may be withdrawn from the formation 117 via the probe assembly114, and this sample may be analyzed using the ionization andspectrometry methods described above, possibly in conjunction with anionization and/or spectrometry device also positioned within the device100 and/or another component of the drill string.

The pump 118 may be used to draw subterranean formation fluid 108 fromthe formation 117 into the testing-while-drilling device 110 by theprobe assembly 114. The fluid may thereafter be expelled through a portinto the wellbore, or it may be sent to one or more fluid analyzersdisposed in a sample analysis module 492, which may receive theformation fluid for subsequent analysis. Fluid analyzers may include oneor more spectrometers and analyzers to interpret spectral datatherefrom, such as to determine fluid composition utilizing theionization and spectrometry methods in accordance with the presentdisclosure. The sample analysis module 106 may also be configured insome embodiments to perform such analysis on fluid obtained from thewellbore and/or drill string. For example, the sample analysis module106 may be configured for use in mud-gas logging operations, wherein gasextracted from mud before and/or after the bit is analyzed to determinecomposition and/or concentrations; as described herein.

The stabilizer blade 110 of the testing-while-drilling device 100 may beprovided with a plurality of sensors 112, 116 disposed adjacent to aport of the probe assembly 114. The sensors 112, 116 may be configuredto determine petrophysical parameters such as saturation levels of aportion of the formation 117 proximate the probe assembly 114. Forexample, the sensors 112 and 116 may be configured to measure electricresistivity, dielectric constant, magnetic resonance relaxation time,nuclear radiation, and/or combinations thereof.

The testing-while-drilling device 100 may include a fluid sensing unit122 through which the obtained fluid samples and/or injected fluids mayflow, and which may be configured to measure properties of the flowingfluid. It should be appreciated that the fluid sensing unit 122 mayinclude any combination of conventional and/or future-developed sensorswithin the scope of the present disclosure.

A downhole control system 104 may be configured to control theoperations of the testing-while-drilling device 100. For example, thedownhole control system 104 may be configured to control the extractionof fluid samples from the formation 117, wellbore and/or drill string,the analysis thereof, and any pumping thereof, for example, via thepumping rate of the pumps 126 and/or 118.

The downhole control system 104 may be configured to analyze and/orprocess data obtained from the downhole sensors and/or disposed in thefluid sensing unit 122 or from the sensors 112, and/or the fluidanalysis module 106. The downhole control system 104 may be furtherconfigured to store measurement and/or processed data, and/orcommunicate measurement and/or processed data to another componentand/or the surface for subsequent analysis.

While the testing-while drilling device 100 is depicted with one probeassembly, multiple probes may be provided with the testing-whiledrilling device 100 in accordance with the present disclosure. Forexample, probes of different inlet sizes, shapes (e.g., elongatedinlets) or counts, seal shapes or counts, may be provided. Wellboretools in accordance with the present disclosure may be designed toinclude the detection components on a logging sonde or drill string.

Turning to FIG. 2, an example well site system according to one or moreaspects of the present disclosure is shown. The well site may besituated onshore (as shown) or offshore. A wireline tool 212 may beconfigured to measure a portion of a wall of a wellbore penetrating asubsurface formation 206. A wireline tool 212 may be suspended in thewellbore 208 from a lower end of a multi-conductor cable 202 that may bespooled on a winch at the surface. Cable 202 may be communicativelycoupled to an electronics and processing system 204. The electronics andprocessing system 204 may include a controller having an interfaceconfigured to receive commands from a surface operator. In some cases,the electronics and processing system 204 may further include aprocessor configured to implement one or more aspects of the methodsdescribed herein.

The example wireline tool 212 may include a tool housing 208 protectingthe internals, a central flow line 210 running through the body of thetool connecting the sample bottle 240 to other components such as fluidpump 238 and probe assembly 228. During operation, a sample 234 may bedrawn into sample inlet and/or injection valve 236 and carried to theanalytical module. The analytical module contains a gas source 214 inconnection with a vaporization chamber 216 and chromatography column 220in line with a thermal conductivity detector (TCD) 222. The massspectrometer module contains the mass analyzer 224, which ispressure-regulated by vacuum pump 226.

Tools in accordance with the present disclosure may be arranged invarious configurations between the gas chromatograph, detector, and massspectrometer. With particular respect to FIG. 3, a flow diagram is shownindicating a possible configuration of a wellbore analysis tool inaccordance with the present disclosure. To begin a downhole measurement,a sample is drawn from the wellbore using a sample acquisition system at302 and, in some embodiments, passed through a filter 304 to removesolid debris and other materials. A gas emitted from a gas source 308 isthen used to carry a sample introduced by the injection valve 310 intothe vaporization chamber 312. The vaporized sample and carrier gas arethen passed through the chromatography column 314 to separate the sampleinto various components.

Depending on the system configuration, the outlet of the gaschromatography column may send the sample to a thermal conductivitydetector 316 for component analysis. The outlet of the thermalconductivity detector may be connected to the inlet of a massspectrometer 318 in some embodiments, which may receive the samplecomponents, along with gas from a source 306. In one or moreembodiments, an ionizable gas such as nitrogen may be added from source306 to increase sample ionization prior to introduction into the massspectrometer module of the wellbore tools.

However, gas supplementation from 306 may be omitted in some embodimentsin which sample volume and carrier gas permit MS measurement. In someembodiments, the thermal conductivity detector may be omitted and thesample may exit the chromatography column 314 and pass directly to theinlet of the mass spectrometer 318. Once the sample passes into the massspectrometer from inlet 318, vacuum generated from a vacuum source 326draws the sample through ionizer 320, into the mass analyzer 322, and toMS detector 324. Following measurement, the sample leaves the system andis discarded as waste gas 328. In one or more embodiments, one or bothof detectors 316 and 324 may be monitored and/or controlled by acomputer processor.

With particular respect to FIG. 4, a flow diagram is shown indicatinganother configuration of a wellbore analysis tool in accordance with thepresent disclosure. To begin a downhole measurement, a sample is drawnfrom the wellbore using a sample acquisition system at 402 and, in someembodiments, passed through a filter 404 to remove solid debris andother materials. A gas emitted from a gas source 408 is then used tocarry a sample introduced by the injection valve 410 into thevaporization chamber 412. The vaporized sample and carrier gas are thenpassed through the chromatography column 414 to separate the sample intovarious components.

As the sample exits the chromatography column 414, the sample may bedivided into two streams. A first stream may be directed to a thermalconductivity detector 430 and discarded as waste gas 432. The secondstream may direct the sample to the inlet of a mass spectrometer 416.Once the sample passes into the mass spectrometer from inlet 416, vacuumgenerated from a vacuum source 426 may draw the sample through ionizer420, into the mass analyzer 422, and to MS detector 424. Followingmeasurement, the sample leaves the system and is discarded as waste gas428. In one or more embodiments, one or both of detectors 430 and 424may be monitored and/or controlled by a computer processor.

With particular respect to FIG. 5, an embodiment of a GC-MS inaccordance with the present disclosure is shown. During operation, aflow line 502 initially contains the sample prior to passage into the GCby injection valve 504. The injection valve 504, as well as the otherinjection valves discussed herein, are rotary valves, although in someexamples other types of valves may be provided. The sample is passagedwith a carrier gas emitted by gas source 506 into vaporization chamber508 and the vaporized sample is separated into various components incolumn 510, which may be heated to maintain vaporization using oven 512.Following passage through the GC module, the vaporized sample componentsare carried into the mass spectrometer component containing a massanalyzer 516 such as a cylindrical ion trap (CIT). Once the sample is inthe mass spectrometer module, the sample is ionized by an ionizationsource 514 such as a glow discharge ionizer (GDI), further separated bythe mass analyzer 516, and passaged to a detector 518 such as a Faradaycup. In some embodiments, the sample exiting the GC module may becombined with an ionizable gas from secondary gas source 524. The massspectrometer may also maintain vacuum during operation using a vacuumpump 520 such as a scroll pump or other vacuum source. Followinganalysis, the sample components may pass into waste line 522 forappropriate disposal or recycling.

FIG. 5 also shows a schematic diagram of various electronic componentsadapted for use in connection with the exemplary fluid analysis samplingin accordance with embodiments of the present disclosure. According toat least one embodiment, a microprocessor 534 generally represents anyform of computing or controlling device capable of performing any numberof logic and/or controlling operations. In many embodiments,microprocessor 534 addresses and controls the operation of the valve504, carrier gas source 506, temperature controller 532, radio frequencygenerator 526 and high voltage (HV) source 524. In some embodiments,microprocessor 534 may also be configured to receive telemetry data fora wellbore under analysis.

Although not specifically illustrated in FIG. 5, the output of referencedetector 518 may be connected to one or more current amplifiers (I/V)528, and/or an analog-to-digital (A/D) converter 530. A currentamplifier 528 may convert the signal detected by detector 518 into avoltage, and/or an A/D converter 530 may convert the analog signal intoa digital one. The resulting signal, which in many embodiments digitallyrepresents the intensity of ion current detected by detector 518, maythen be supplied to microprocessor 534 for use in computing the peakareas of the MS, FID or TCD spectrum of the vaporized fluid (gas)sample. Thus, in accordance with the signals supplied by the MS, TCD orFID, microprocessor 534 computes the presence and/or amount of any of anumber of chemical compositions in vaporized fluid or gas sample.

Although the foregoing descriptions of FIG. 5 have been provided withreference to discrete elements and circuits, one of skill in the arthaving the benefit of this disclosure will recognize that one or more ofthese discrete circuits may be combined into a single integrated circuitor chip. For example, while transimpedance amplifier 528 and A/Dconverter 530 have been illustrated as discrete elements, the functionof these two circuits may be combined into a single integrated circuit,resulting in increased savings in space and efficiency. The temperatureand operation of the column 510 in oven 512 may be controlled bytemperature controller 532, which may in turn be controlled bymicroprocessor 534.

With respect to FIG. 6.1, a first view of a quadrupole mass analyzer inaccordance with embodiments of the present disclosure is shown. Theinterior of the mass analyzer contains an arrangement of fourcylindrical electrodes with two electrodes 602 connected to negativepolarity DC−RF voltage supply, and the remaining electrodes 604connected to positive polarity DC+RF voltage. With particular respect toFIG. 6.2, a cross-section of the quadruple mass analyzer is shown duringoperation. A sample entering the mass analyzer is converted to ions byionization source 606 and passaged into the channel created by positiveelectrodes 604 and negative electrodes 602, where the trajectory of theions are modified, depending on molecular weight or conformation, forexample, in a RF voltage-dependent fashion. Following separation by thearranged electrodes, the separated ions pass to detector 608.Representative ion trajectories are shown at 610.

With respect to FIG. 7, a quadrupole ion trap mass analyzer is shown. Asample entering the mass analyzer encounters an ionization source 702and the resulting ions are passed into the field of ring electrode 704having end caps 706. Once charged ions enter the mass analyzers, ionsare circulated in the space within the center of the electrode, and theRF voltage supply 708 is modulated to selectively emit ions that arepassed to detector 710 in a controlled fashion. A representative iontrajectory is shown at 715.

With respect to FIG. 8, an exploded view of a cylindrical ion trap (CIT)mass analyzer is shown in accordance with embodiments of the presentdisclosure. A sample entering the CIT passes the ionization source 802,end cap 804, and through a plurality of ring electrodes 806 andinsulators 808 before reaching the detector 812. The CIT mass analyzeris controlled by an RF voltage supply 810 that may be modulated toresolve molecular species of varying weights and conformations.

In one or more embodiments mass spectrometers may operate undertemperature ramp or constant temp operational modes. In someembodiments, variables such as vacuum strength or RF may be adjusted tooptimize the outcome of each measurement. Furthermore, to expand thedetection range, the sample concentration can be reduced by dilution orother methods. Adaptations can be done automatically as a gradual or astepwise change.

In one or more embodiments, wellbore measurements may be obtained byadjusting pressure within the mass analyzer of the MS depending on theconcentration of molecules that is measured. With particular respect toFIG. 9, pressure may be iteratively modified in order to increase theanalytical output from the sample. In one or more embodiments, pressuremay be set to an initial value such as 0.1 Torr at 902. The sample maythen be measured at 904 to determine mass concentration. Pressure maythen be increased at 906 and then mass concentration may be determinedat 904 through a number of iterations represented by 908.

The MS receives the separated components from the GC in a predictableorder, often in which components become heavier and in lowerconcentration as a function of time. However, method in accordance withthe present disclosure may account for anomalies from this pattern suchas the presence of aromatic or branching components that may traveldifferently that the linear alkane counterparts, and the presence ofvarious contaminants from mud filtrates and other wellbore fluidadditives. In one or more embodiments, algorithms may be developed inwhich the RF frequency of the mass analyzer is adjusted following one ormore mass spectrum measurements to increase sensitivity and resolutionof individual components in mixtures eluted from the GC. For example iontrap and quadrupole mass analyzers are operated by applying acombination of RF and DC voltages to the electrodes of the respectivemass analyzer to create a quadrupole electric field. This electric fieldtraps ions in a potential energy well at the center of the analyzer. Themass spectrum is then acquired by scanning the RF and DC fields todestabilize low mass to charge ions. Destabilized ions are ejectedthrough a hole in one endcap electrode and strike a detector, whichallows a mass spectrum to be generated by scanning the fields so thations of increasing m/z value are ejected from the cell and detected.

With particular respect to FIG. 10, a workflow for iteratively adjustingthe RF of a mass analyzer in order to analyze heavier components isshown. However, at different RF frequencies the fragmentation patternmight be different too. In some embodiments, two or more RF may be usedintermittently during operation in order to determine if altering the RFpresents a differing fragmentation pattern that enables additionalcompounds to be resolved. For example, during measurement, the MS may beoperated at a RF frequency suitable for detecting low mass components at1002. Following the initial measurement, the mass of the samplecomponents is determined at 1004, and the RF frequency is lowered at1006, and mass is again determined at 1004. The RF modulation and massdetermination may be performed iteratively according to 1008 until theoperator is satisfied that all components of the sample have beenidentified and/or the error has been lowered to an acceptable lever.Furthermore, other variables like vacuum strength can be adjusted tooptimize the outcome of each measurement. Furthermore, to expand thedetection range the sample concentration can be reduced by dilution orother methods. All these automatic adaptations can be done automaticallyas a gradual or a stepwise change.

In the following section, the individual components of wellboremeasurement tools will be discussed in greater detail in the followingsections.

Gas Chromatograph

Gas chromatographs (GC) in accordance with the present disclosure may beinstalled within a wellbore tool as discussed above with respect toFIGS. 1 and 2. GC devices may contain a gas source that generates andmaintains an inlet pressure for the gas chromatograph between 750 to4500 Torr in some embodiments. Carrier gases include inert gases such ashelium, hydrogen provided from a compressed gas cylinder or chargedmetal hydrides. Carrier gas sources may include a fraction of anionizable gas such as nitrogen that is included at a concentration of0.1% to 10% by volume of the total carrier gas in some embodiments, andfrom 1% to 3% in some embodiments.

Gas Chromatograph Detectors

GC in accordance with the present disclosure may include a thermalconductivity detector to analyze gaseous and fluid components. TCDdetectors may be limited to certain carrier gases such as helium orhydrogen and may be unable to differentiate some components in a sample.TCDs may also have a lower detection limit of about 500 ppm.

In one or more embodiments, systems in accordance with the presentdisclosure may operate under work under reduced pressure and downholetemperatures. Systems may contain a gas chromatograph, a TCD, and a highpressure (>10⁻³ bar) mass spectrometer. In some embodiments, systems maybe designed to fit within a tool that may be emplaced within a wellbore,including as part of a tool string.

In one or more embodiments, the inlet of the TCD may be connected to theoutput of the GC column. In some embodiments, the inlet of the MS may beconnected to the outlet of the TCD or directly from the GC. MS inaccordance with the present disclosure may contain an ionizer, a massanalyzer, and an ion detector. The mass analyzer of the MS may be an iontrap analyzer in some embodiments, or a quadrupole mass analyzer inother embodiments. Connections between the individual components may begas- or fluid-tight seals suitable for the application.

Mass Spectrometer

In one or more embodiments, devices in accordance with the presentdisclosure may include high pressure mass spectrometers such asquadrupole and ion trap mass spectrometers. MS in accordance with thepresent disclosure often contain several components, including an inlet,an ion source, a mass analyzer, and an ion detector. In some embodiment,MS may include a controller to activate the detector, one or more pumps,and a vacuum system to maintain pressure levels. Vacuum systems mayinclude scroll pumps, a hydrogen generator such as metal hydride or acombination of both.

In one or more embodiments, the vacuum system may generate a pressure inan MS between the 0.001 Torr and 10 Torr and capable of handling aninlet pressure for the mass spec which is below 600 Torr. In someembodiments, a flow restrictor maybe placed between the outlet of theTCD and the mass spectrometer to maintain pressure at the TCD. MS inaccordance with the present disclosure may include a second gas sourcewith an ionizable gas such as nitrogen that is added just before themass spectrometer. For example, after the TCD if the MS is connected tothe outlet of TCD or after the column if the mass spectrometer isdirectly connected to the outlet of the column. MS in accordance withthe present disclosure may operate at in a pressure regime that rangesfrom 10⁻³ to 10 Torr in some embodiments, and from 10⁻² to 10 Torr inother embodiments.

Ion Sources

MS in accordance with the present disclosure may include an ionizer thationizes the incoming analyte from the GC. Ionizers may include a softionizers that remove a single electron from molecules within the analyteand attempt to minimize molecule fragmentation, creating what is oftenreferred to as a singly-charged molecular ion. In one or moreembodiments, additional gas that can easily be ionized may be added tothe analyte prior to passage to the ionizer to increase the degree ofsample ionization. In some embodiments, nitrogen may be used to inducechemical ionization of the analyte.

Soft ionization techniques such as glow discharge ionization,electrospray ionization, photionization, electron ionization, andchemical ionization, may be used in devices in accordance with thepresent disclosure to produce ions from hydrocarbons and other analytes,and are discussed in further detail below.

A glow discharge ionization source includes a discharge chamber havingan entrance orifice for receiving the analyte particle beam or analytevapors, and a target electrode and discharge electrode therein. Anelectric field applied between the target electrode and dischargeelectrode generates an analyte ion stream from the analyte vapor, whichis directed out of the discharge chamber through an exit orifice andinto a mass analyzer.

In electro spray ionization, a sample solution enters an electrospraychamber through a hollow needle which is maintained at a few kilovoltsrelative to the walls of the electrospray chamber. The electrical fieldcharges the surface of the liquid emerging from the needle, dispersingit by coulomb forces into a spray of fine, charged droplets. At thispoint the droplets become unstable and break into daughter droplets.This process is repeated as solvent continues to evaporate from eachdaughter droplet. Eventually, the droplets become small enough for thesurface charge density to desorb ions from the droplets into the ambientgas. These ions, which include cations or anions attached to solvent orsolute species which are not themselves ions, are suitable for analysisby a mass spectrometer.

Photon Ionization is another ionization technique in which analytesabsorb light (typically a single photon in the vacuum ultravioletrange), and that photon energy is used to eject an electron. If thephoton energy is just above the ionization potential, little energy willbe leftover for fragmentation, providing soft ionization.

In electron ionization, an electron beam is directed at theanalyte-containing sample. Some of the translational energy of theelectrons is used to ionize the analytes. Typically 70 eV electrons areused, but that energy is much greater than typical ionization potentials(around 10 eV), and that excess energy typically leads to extensivefragmentation. Using low electron energy (around 15 eV) produces fewerfragments with less ionization efficiency.

In chemical ionization various gases are first ionized (using electronionization for example), and those ionized gases are allowed to reactwith an analyte. Interaction with ionized gases may impart an electricalcharge to the analyte, which is then passed into the mass analyzer. Theefficiency of this process may vary greatly for different analytes,providing a contrast mechanism in some cases. On the other hand,chemical ionization techniques may result in the formation of complexesbetween the analyte and the ionization gas, which can obscure analysisresults.

Mass Analyzers

Mass spectrometers in accordance with the present disclosure may includemass analyzers such as ion traps, linear and ion trap quadrupole, andLoeb-Eiber filters.

Quadrupole mass spectrometers (QMS) are designed from four cylindricalrods electrically connected to RF and DC voltage sources as discussedabove with respect to FIGS. 6.1 and 6.2. The RF to DC ratio allowsselective transmission of ions of a particular m/z value to travel in astable trajectory along the z-axis. A mass spectrum is obtained byramping the amplitude of the RF and DC voltages to sweeps ions ofincreasing m/z toward the detector.

A quadrupole ion trap (QIT) mass analyzer operates according to similarprinciples as a QMS, but may allow ions of multiple m/z values to betrapped simultaneously in a region of stability defined by solutions ofthe Mathieu equations described by, in some embodiments, the parametersq_(z)=4zV/mr²ω² and a_(z)=−8zU/mr²ω² where z is the electric charge, Vthe amplitude of the RF voltage, U is the amplited of the DC voltage, mis the mass of the ion, r is the radius of the ion trap, and co is theangular frequency of the RF potential. QIT mass analyzers in accordancewith the present disclosure may eject trapped ions oscillating atfrequencies proportional to the fundamental frequency ω when operatingin mass selective instability mode, in sequence from low to high m/zvalues along the q_(z) axis, with the DC potential held at zero, byramping the amplitude of the RF voltage as q_(z) approaches 0.908whereupon they are ejected, as discussed above with respect to FIG. 7.

Cylindrical ion trap (CIT) mass analyzers may be function similarly tothe QIT, with the exception that hyperbolic electrodes of the QIT arereplaced by a flat ring electrode. In some embodiments, miniaturized CITmass analyzers may compensate for the loss of trapping capacityresulting from the smaller trap radius by including an array of trapswith identical radii, as discussed above with respect to FIG. 8 and inthe examples below.

Mass analyzers may also include Loeb-Eiber filter such as thosedescribed in U.S. Pat. No. 7,772,546. Loeb-Eiber filters may be suitedfor operation at relatively high pressures. In one or more embodiments,the collisional dampening of ions up to the mass filter thermalizes thekinetic energy of the ions which makes the filtering more effective. Insome embodiments, Loeb-Eiber filters may be fabricated using traditionalmanufacturing techniques or MEMS technology.

Detectors

Mass spectrometers in accordance with the present disclosure mayincorporate one or more detectors that measure ionized analytecomponents. Detectors may measure ions based upon their charge ormomentum. In one or more embodiments, detectors may include a Faradaycup that measures ion current traveling through the mass analyzers ofthe mass spectrometer. Other detectors may include electron multipliers,channeltrons and multichannel plates.

Applications

GC-MS tools in accordance with the present disclosure may be operated ina number of modes depending on the application. In one or moreembodiments, data output may be formatted as total ion current (TIC)chromatographs representing the summed intensity across the entire rangeof masses being detected at during every measurement collected duringthe analysis. In some embodiments, data output may take the form of aselected-ion monitoring (SIM) chromatogram representing a single m/zvalue or subrange of values measured over the duration of sampleanalysis.

Low Concentration Analyte Detection

Methods in accordance with the present disclosure may increase thesensitivity of a mass spectrometer operating in TIC mode or SIM mode. Inone or more embodiments, GC-MS in accordance with the present disclosuremay possess detection limits in the range of single digit ppm. In someembodiments, a wellbore tool incorporating a GC-MS in accordance withthe present disclosure may be used to detect sample concentrations at aconcentration in the range of 1 ppm or greater.

GC-MS tools in accordance with the present disclosure may be used todetermine analyte concentration by generating a chromatogram that isthen used in combination with a calibration curve obtained from areference analyte of known concentration. For example, a series ofcalibration samples may be measured using a GC-MS operating undersimilar conditions expected downhole, and the peak areas from theresulting chromatographs may be used to determine the concentration ofthe respective analyte in an unknown sample.

In one or more embodiments, GC-MS in accordance with the presentdisclosure may be employed for the detection of sulfur components withina wellsite operating environment. The concentration of sulfurcomponents, such as hydrogen sulfide, as low as 5 ppm may be harmful tooperators and installed equipment. In some embodiments, determination ofthe concentration of sulfur components may be monitored to ensure theproper level of corrosion resistance is maintained when selectingcompletions and uphole equipment. Methods in accordance with the presentdisclosure directed to monitoring the presence of sulfur components mayinclude the use of selected-ion monitoring (SIM) in the range of 32-34m/z to identify and quantify the various components. Concentration ofsulfur components may be determined, for example, by establishing acalibration curve for a selected analyte as discussed above.

GC Peak Deconvolution

In one or more embodiments, methods in accordance with the presentdisclosure may be used to deconvolve overlapping peaks output in a GCchromatogram. During measurement, components having similar mass ormolecular shape may elute from the GC at the same time as othercomponents, which may appear in a chromatogram as a single peak.However, methods in accordance with the present disclosure may be usedto resolve the components on the basis of mass, chemical structure,fragmentation or addition patterns using mass spectroscopy.

Chromatogram deconvolution methods in accordance with the presentdisclosure may include measuring a sample and obtaining a gaschromatogram output. The eluted fraction corresponding to the combinedsample peaks is then analyzed using a mass spectrometer, which outputsthe molecular weights of the co-eluting components. In some embodiments,the ratio of the peak intensity of the components may be used for rapiddetection using GC-MS to determine the ratio between two or morecomponents that elute at the same time from a chromatograph. Forexample, the relative signal intensities of the components in the outputof the mass spectrometer may then be used as an indicator of therelative contribution of each component to the peak observed in the gaschromatogram.

In one or more embodiments, the ratio of two components obtained fromthe output of the mass spectrometer may be used in conjunction with theoutput of a TCD to establish concentrations for each of the components.For example, in a case where two components are distinguishable by MSchromatogram, but register as a single peak on a TCD chromatogram, theratio of the two components may be used to allocate the concentrationbetween the two components. In practice, the components are alsoidentified, such as by matching of the fragmentation patterns to anexisting library of identified components by MS, and the known molarmass of the components are used to derive a concentration. Similarly, inthe case in which a peak is too small to be determined by the TCD, butis proximate to a peak detectable by the TCD, the ratio of these twopeaks can then be used to estimate a concentration for the component inthe smaller peak by relating it to the TCD measurement.

In some embodiments, the determination of concentration from a ratio oftwo components identified by MS may be performed by determining relativeconcentration between two components of the sample based on the outputof the mass spectrometer, identifying the two components by matching theoutput of the mass spectrometer to a library of known components,determining a combined concentration of the two components of the samplebased on the output of a thermal conductivity detector configured toreceive an output from the gas chromatograph, and determining aconcentration for the two components using the identity of the twocomponents, the relative concentration of the two components, and thecombined concentration of the sample based on the output of a thermalconductivity detector.

In one or more embodiments, methods in accordance with the presentdisclosure may be adapted for group analysis of multiple components. Insome embodiments, group analysis may utilize SIM to separate and analyzecomplex grouping of components. For example, aromatic species may allexhibit a GC peak representative of the benzene ring at 78 m/z or incombination with nitrogen addition at 106 m/z. The analysis ofcomponents within this range may then be separated on the basis ofmolecular weight, selective ionization, and fragmentation patterns usinga mass spectrometer in accordance with the present disclosure. Groupanalysis may also be applied to other component mixtures such aspolyaromatics, heteroatomic rings containing sulfur and oxygen, and thelike.

In one or more embodiments, the ionization method may be tuned toselectively ionize a particular type of analyte. For example, N-alkaneswill have a distinct peak in the TCD spectrum, whereas their visibilityin a total ion count chromatogram will be suppressed due to theinefficient ionization process of the n-alkanes. In contrast, thebranched alkanes often show up as broad overlapping peaks in the TCDresults, but can give a stronger more defined peak in the total ioncount chromatogram. In one or more embodiments, selection of theionization technique may be used in combination with a TCD to identifythe branched alkane and n-alkane components.

The ratio of specific components in a hydrocarbon stream may also beused in some embodiments to detect connectivity between zones, such aswhere the ratio of the components is characteristic to one or morerespective zones. For example, if an oilfield a single zone, then thecomposition of the oil is expected to be in equilibrium and the ratiosbetween components with similar molar mass should be relativelyhomogeneous as a function of depth and within neighboring wells in thefield. However, variations in the molar mass ratios between two samplingpoints may signify that the fluids are not in equilibrium, which mayalso indicate the presence of barriers between zones. By way of example,Halpern C7 correlations may be used to differentiate samples throughdifferences in the ratios between the five substituted pentanes with atotal of seven carbon atoms, i.e. 2,2-dimethyl pentane, 2,3-dimethylpentane, 2,4-dimethyl pentane, 3,3-dimethyl pentane, and 3-ethylpentane.

Biodegradation Characterization

Methods in accordance may be used to quantify the level ofbiodegradation in a hydrocarbon sample, and enable the selection ofpseudocomponents in cases in which the GC chromatogram is ambiguous orpoorly defined. The selection of pseudocomponents in hydrocarbonmixtures and other non-biodegraded oils may have characteristic peaksthat allow grouping of the various components into pseudocomponentshaving similar boiling points and carbon number, but slight variation inmolecular weight, branching, functionalization, and the like. In GCanalysis, pseudocomponents are defined as the all components elutingafter n-Cn to, and including, n-C(n+1).

However, alkanes and other organics may undergo biodegradation byvarious microorganisms within a reservoir, decreasing the number ofn-alkanes and generating a number of byproducts. As an example, arepresentative oil sample with little or no biodegradation as evidencedby the distinguishable carbon number peaks is shown in FIG. 11. Bycomparison, a biodegraded oil sample is shown in FIG. 12 in whichdegradation products obscure the carbon number peaks and render peakidentification more difficult. Biodegradation can interfere with theability to identify pseudocomponents, particularly as the n-alkanes usedas distinct chromatographic landmarks for the grouping ofpseudocomponents are the first to be reduced in concentration bybiodegradation. In one or more embodiments, MS chromatograms may be usedto identify elution times and other landmarks that can be used to definepseudocomponent boundaries.

Library Matching with Background Subtraction

In one or more embodiments, methods may include the analysis of complexcomponent mixtures using comparison of GC-MS output to compiled librarydata for the expected chemical components in the sample. In someembodiments, use of library matching may enable the quantification ofthe co-eluting components. Library matching methods may distinguishcomponents having the same mass on the basis of varied fragmentation insome embodiments. Further, library matching methods may allow thesubtraction of molecular weights and fragmentation patterns of knowncomponents from a chromatogram output, which may enable an operator toisolate and identify novel and unknown components in a sample.

Applications of library matching in accordance with the presentdisclosure may include comparing the measured response from a GC-MS to alibrary including known chemical components to aid in identification ofknown analytes in a sample, including the quantification of molecularweight and concentration of individual analytes. Methods in accordancewith the present disclosure that utilize library matching may includethe establishment of a library of chemical components from existing andprojected GC-MS chromatograms. However, while described as a startingpoint, a chemical library may be assembled at any stage in the analysis,including after the initial sample measurement downhole.

EXAMPLES

In the following examples, an analyte is measured using a high-pressuregas chromatograph/mass spectrometer combination tool and MS is used toincrease the accuracy of component identification and deconvolvemultiple overlapping peaks in some instances.

A sample taken from the headspace of a dead oil sample containinghydrocarbon mixtures of components C1 to C8 and measured using a GC-MSin accordance with the present disclosure. The GC component of thedevice utilized an alumina BOND/Na₂SO₄ column and is using helium as acarrier gas. The MS component was equipped with a glow discharge ionizerand a miniature ion trap mass analyzer, and a faraday cup detector.During operation, the GC column was cycled at 60° C. for 2 minutes, thenheated to 200° C. at 10° C./min for 10 minutes. The MS ion trap wasoperated at a starting RF of 6.97 MHz and an internal operating pressureof 3 Torr. The MS measurements were done with a frequency of 2measurements per second with every measurement averaging 15 mass scansat each of the three RF frequencies.

With particular respect to FIG. 13, a diagram for the total ion count(TIC) for the sample is shown at a frequency of 6.97 MHz. Withparticular respect to FIG. 14, the specific ion measurement at 58 m/z isshown for the same sample. FIG. 15 also shows the sample measured inFIG. 14 with the total ion count according to a logarithmic scale. Withparticular respect to FIG. 16, the GC fraction at 655-660 seconds, whichcorrelates to C6 hydrocarbons, is analyzed with MS at 58 m/z, 70 m/z,and 86 m/z. The results demonstrate that it is possible to deconvolvethe co-eluting fractions between 655 and 660 seconds from the GC.Furthermore, the spectrum demonstrates that it is possible todistinguish n-C6 at 680 seconds from the other C6 isomers by observingthe particular fragmentation pattern.

In the next example, combined GC-MS is used to resolve the peaks for thesame sample. The specific ion measurement is shown for the C7 fractionfrom the GC at 58 m/z, 72 m/z, 86 m/z, and 100 m/z are shown in FIG. 17.With particular respect to FIGS. 18-20, the mass spectrum of three C7components eluting at 786, 792, and 797 seconds, respectively, are shownto demonstrate the ability of a GC-MS to resolve species that wouldoverlap if a column or temperature regime is used with less resolvingpower than the current measurement. For example, overlap in spectra maybe expected in cases in which downhole conditions involve high ambienttemperatures and cooling is more difficult.

In accordance with some examples, applicant has discovered that byproviding and combining certain features, including a rotary valve andan ion trap or quadrupole mass analyzer, it is possible to operate amass spectrometer at high pressures (greater than 10⁻² Torr). This inturn allows for more robust pumps (e.g., scroll pumps, screw pumps,piston pumps) which are—in contrast to typical mass spectrometrypumps—suitable for use in downhole conditions in a wellbore. It isfurther noted in this regard that the ion trap and quadrupole massanalyzers are scalable to small sizes that reduce the increasedmolecular collisions that occur due to higher pressures.

Although the preceding description has been described herein withreference to particular means, materials and embodiments, it is notintended to be limited to the particulars disclosed herein; rather, itextends to all functionally equivalent structures, methods and uses,such as are within the scope of the appended claims. In the claims,means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, although anail and a screw may not be structural equivalents in that a nailemploys a cylindrical surface to secure wooden parts together, whereas ascrew employs a helical surface, in the environment of fastening woodenparts, a nail and a screw may be equivalent structures. It is theexpress intention of the applicant not to invoke 35 U.S.C. § 112(f) forany limitations of any of the claims herein, except for those in whichthe claim expressly uses the words ‘means for’ together with anassociated function.

To the extent used in this description and in the claims, a recitationin the general form of “at least one of [a] and [b]” should be construedas disjunctive. For example, a recitation of “at least one of [a], [b],and [c]” would include [a] alone, [b] alone, [c] alone, or anycombination of [a], [b], and [c].

1. A method comprising: emplacing a wellbore tool in a wellbore, thewellbore tool containing a gas chromatograph, a rotary valve configuredto inject a fluid sample into the gas chromatograph, and a massspectrometer, wherein the mass spectrometer is configured to operate ata pressure greater than 10⁻² Torr, wherein an inlet for the massspectrometer receives an output from an outlet of the gas chromatograph,and wherein the mass spectrometer comprises at least one of (a) an iontrap analyzer and (b) a quadrupole mass analyzer; measuring a samplefrom the wellbore using the wellbore tool; and determining a molecularweight of one or more components of the sample from the measuredresponse of the wellbore tool.
 2. The method of claim 1, furthercomprising determining a concentration for the one or more components ofthe sample by comparing the measured response of the wellbore tool witha calibration curve established for the one or more components.
 3. Themethod of claim 1, further comprising: determining relativeconcentration between two components of the sample based on the outputof the mass spectrometer; identifying the two components by matching theoutput of the mass spectrometer to a library of known components;determining a combined concentration of the two components of the samplebased on the output of a thermal conductivity detector configured toreceive an output from the gas chromatograph; determining aconcentration for the two components using the identity of the twocomponents, the relative concentration of the two components, and thecombined concentration of the sample based on the output of a thermalconductivity detector.
 4. The method of claim 1, wherein measuring asample from the wellbore tool comprises separating the sample into oneor more eluted fractions using the gas chromatograph, and wherein themethod further comprises deconvolving the one or more eluted fractionsinto one or more deconvolved chromatograph peaks using the molecularweights determined for the one or more components of the samplecorresponding to the one or more eluted fractions.
 5. The method ofclaim 4, wherein the ratio of the integrated area for deconvolvedchromatograph peaks is used to determine the relative concentration ofthe one or more components of the fluid.
 6. The method of claim 4,wherein the one or more deconvolved chromatograph peaks comprisearomatics.
 7. The method of claim 1, wherein the mass spectrometercomprises a soft ionization source, and wherein the method furthercomprises deconvolving branched alkanes, cycloalkanes, and n-alkaneseluted from a gas chromatograph by selectively ionizing the branchedalkanes with the soft ionization source and determining the molecularweights for the branched alkanes.
 8. The method of claim 1, furthercomprising separating one or more components of the sample into one ormore pseudocomponents.
 9. The method of claim 1, wherein the massspectrometer is configured to detect a sample component at aconcentration in the range of 1 ppm or greater.
 10. The method of claim1, wherein the mass spectrometer is configured to monitor a mass windowin the range of 32-34 m/z and to output a selected-ion monitoringchromatogram.
 11. The method of claim 1, wherein the mass spectrometeris configured to detect one or more sulfur components.
 12. The method ofclaim 1, wherein the mass spectrometer comprises an ion trap massanalyzer.
 13. The method of claim 1, wherein the mass spectrometercomprises a quadrupole mass analyzer.
 14. A method comprising:establishing a library of one or more chemical components; emplacing awellbore tool in a wellbore, the wellbore tool containing a gaschromatograph, a rotary valve configured to inject a sample into thechromatograph, and a mass spectrometer, wherein the mass spectrometer isconfigured to operate at a pressure greater than 10⁻² Torr and whereinthe mass spectrometer comprises at least one of (a) an ion trap analyzerand (b) a quadrupole mass analyzer; measuring a sample from the wellboreusing the wellbore tool; comparing the measured response from thewellbore tool for the sample with results from the library of one ormore chemical components; and determining a molecular weight of one ormore components of the sample.
 15. The method of claim 14, furthercomprising determining a concentration for the one or more components ofthe sample by comparing the measured response of the wellbore tool forthe sample with a calibration curve established for the one or morecomponents.
 16. The method of claim 14, wherein the mass spectrometer isconfigured to detect a sample component at a concentration in the rangeof 1 ppm or greater.
 17. The method of claim 14, further comprisingdetermining the concentration the one or more components of the fluid bycomparing the measured response from the wellbore tool with acalibration curve established for the one or more components.
 18. Themethod of claim 14, wherein the mass spectrometer comprises a softionization source, and wherein the method further comprises deconvolvingbranched alkanes, cycloalkanes, and n-alkanes eluted from a gaschromatograph by selectively ionizing the branched alkanes with the softionization source and determining the molecular weights for the branchedalkanes.
 19. The method of claim 14, wherein the mass spectrometercomprises an ion trap mass analyzer.
 20. The method of claim 14, whereinthe mass spectrometer comprises a quadrupole mass analyzer.
 21. Themethod of claim 14, wherein the mass spectrometer is configured todetect one or more sulfur components.
 22. The method of claim 14,wherein measuring a sample from the wellbore tool comprises separatingthe sample into one or more eluted fractions using the gaschromatograph, wherein the method further comprises deconvolving the oneor more eluted fractions into one or more deconvolved chromatographpeaks using the molecular weights determined for the one or morecomponents of the sample corresponding to the one or more elutedfractions, and wherein the one or more deconvolved chromatograph peakscomprise aromatics.